1. Field of the Invention
The present invention relates to a process for treating acetate-based films, particularly those having a magnetic particle layer onto which a sound track has been recorded, so that information recorded on the film can be reproduced.
2. Description of Related Art
Traditionally, the motion picture industry has prepared and stored picture and sound masters separately until a composite print is made for release. Beginning in the early 1950's, sound masters for recording the sound tracks to motion pictures were made on acetate-based films having a layer of magnetic particles adhered thereto by a binder (hereinafter referred to as "magnetic acetate-based film"). The magnetic particle layer allows the sound track to be edited, erased, or recorded over as the sound track is produced. In addition, whenever a reproduction of the sound track is desired, the sound master is run through, e.g., a magnetic reproducer, referred to more generally herein as a "sound transfer device," which reproduces the sound track(s). Currently, up to six channels of recorded information may be present on a sound master, and all must have intimate contact with the playback head to insure that the reproduction will faithfully reproduce all of the frequencies on the sound master.
Today, it is well known that acetate-based films should be stored in a cool and dry environment, preferably at a temperature from about 50.degree. to 60.degree. F. and a relative humidity of less than about 50 percent. However, when magnetic acetate-based films first began to be used, this was not well understood, nor was it appreciated what effect the passage of time had on the film's physical properties if the film was not stored properly. For example, acetate-based films are now known to have an affinity for water, which may cause them to distort if they are not stored under proper conditions. Consequently, adequate care often was not taken to ensure that acetate-based films were stored under conditions that would enable the information recorded on the film to be reproduced years later.
Many rolls of magnetic acetate-based film still in existence today cannot be put through a sound transfer device satisfactorily because of warpage caused by dehydration or temperature instability due to improper storage. This warpage may take the form of "cupping" or "curling," sometimes also referred to as "crowning," or it may be longitudinal warpage. These types of physical distortion interfere with obtaining the required intimate contact between the playback head and the surface of the film contacting the playback head. Moreover, exposure of acetate-based films to either heat or humidity tends to accelerate the deterioration process, and once this deterioration starts, there is no method currently known to slow it down or stop it before the acetate layer ultimately deteriorates.
A related problem with magnetic acetate-based films that have not been properly stored is that such films may have deteriorated to the point where the binder that adheres the magnetic particle layer to the acetate layer no longer performs this function adequately. This means that the magnetic particle layer begins to separate from the acetate layer, leaving a pile of magnetic particles at the bottom of the film container. Such films are unstable and difficult to handle, and if too much of the magnetic layer is lost, the information recorded thereon is also lost. The unpredictability of such binders also makes the use of chemical reagents for flattening the film particularly undesirable.
Prior to the present invention, the only way that sound tracks recorded on a physically distorted magnetic acetate-based film could be reproduced was to contact the film with a "pressure pad" at the point where the film passes over the playback head in a sound transfer device. A steady pressure would then be applied to the pressure pad to force the film to conform to the contours of the playback head as the film passed over the head. The application of sufficient pressure to a film that is not excessively physically distorted will cause the film to conform better to the contour of the playback head, and an acceptable, albeit sometimes marginal, reproduction can be produced by this prior art method. This method also allows the sound track to be transferred to another, preferably more stable substrate, such as a polyester film, that is known to be non-reactive with water when stored at room temperature. Care must be taken, however, not to apply too much pressure, as that can distort the true film path and can also cause vibrations of the film that will modulate the recorded sound, thus making the reproduction useless. Also, in those instances where the acetate-based film has become severely cupped or curled, it has not been possible to apply sufficient pressure without causing these types of undesirable consequences. Since the necessary intimate contact between the film and the playback head cannot be obtained in such instances, an excessively physically distorted sound master has been virtually useless. This means that prior to the present invention, the information recorded on such sound masters was lost forever.
Accordingly, the need exists for a method of treating acetate-based films, particularly acetate-based films having a magnetic particle layer onto which a sound track is recorded, so that information recorded on such films can be reproduced even when a film has been distorted by heat or humidity, or both.